1. Field of the Invention
In one of its aspects, the present invention relates to an antifouling surface—e.g., a quartz element having an antifouling surface. In another of its aspects, the present invention relates to a radiation source assembly comprising the antifouling surface. In yet another of its aspects, the present invention relates to a radiation source module comprising the antifouling surface. In yet another of its aspects, the present invention relates to a fluid treatment system comprising the antifouling surface. In another of its aspects, the present invention relates to a method of producing an antifouling surface—e.g., a quartz element having an antifouling surface. Other aspects of the invention will become apparent to those of skill in the art upon reviewing the present specification.
2. Description of the Prior Art
Fluid treatment systems are known generally in the art.
For example, U.S. Pat. Nos. 4,482,809, 4,872,980 and 5,006,244 [all in the name of Maarschalkerweerd and hereinafter referred to as the Maarschalkerweerd #1 Patents] all describe gravity fed fluid treatment systems which employ ultraviolet (UV) radiation.
Such systems include an array of UV lamp frames which include several UV lamps each of which are mounted within sleeves which extend between and are supported by a pair of legs which are attached to a cross-piece. The so-supported sleeves (containing the UV lamps) are immersed into a fluid to be treated which is then irradiated as required. The amount of radiation to which the fluid is exposed is determined by the proximity of the fluid to the lamps, the output wattage of the lamps and the fluid's flow rate past the lamps. Typically, one or more UV sensors may be employed to monitor the UV output of the lamps and the fluid level is typically controlled, to some extent, downstream of the treatment device by means of level gates or the like.
Depending on the quality of the fluid which is being treated, the sleeves surrounding the UV lamps periodically become fouled with foreign materials, inhibiting their ability to transmit UV radiation to the fluid. For a given installation, the occurrence of such fouling may be determined from historical operating data or by measurements from the UV sensors. Once fouling has reached a certain point, the sleeves must be cleaned to remove the fouling materials and optimize system performance.
If the UV lamp modules are employed in an open, channel system (e.g., such as the one described and illustrated in Maarschalkerweerd #1 Patents), one or more of the modules may be removed while the system continues to operate, and the removed frames may be immersed in a bath of suitable cleaning solution (e.g., a mild acid) which may be air-agitated to remove fouling materials. This practice was regarded by many in the field as inefficient, labourious and inconvenient.
In many cases, once installed, one of the largest maintenance costs associated with prior art fluid treatment systems is often the cost of cleaning the sleeves about the radiation sources.
U.S. Pat. Nos. 5,418,370, 5,539,210 and RE36,896 [all in the name of Maarschalkerweerd and hereinafter referred to as the Maarschalkerweerd #2 Patents] all describe an improved cleaning system, particularly advantageous for use in gravity fed fluid treatment systems which employ UV radiation. Generally, the cleaning system comprises a cleaning carriage engaging a portion of the exterior of a radiation source assembly including a radiation source (e.g., a UV lamp). The cleaning carriage is movable between: (i) a retracted position wherein a first portion of radiation source assembly is exposed to a flow of fluid to be treated, and (ii) an extended position wherein the first portion of the radiation source assembly is completely or partially covered by the cleaning carriage. The cleaning carriage includes a chamber and seals in contact with the first portion of the radiation source assembly. The chamber is supplied with a cleaning solution (typically an acidic cleaning solution) suitable for removing undesired materials from the first portion of the radiation source assembly.
The cleaning system described in the Maarschalkerweerd #2 Patents represented a significant advance in the art, especially when implemented in the radiation source module and fluid treatment system illustrated in these patents.
In recent years, there has been interest in the so-called “transverse-to-flow” fluid treatment systems. In these systems, the radiation source is disposed in the fluid to be treated in a manner such that the longitudinal axis of the radiation source is in a transverse (e.g., orthogonal vertical orientation of the radiation sources) relationship with respect to the direction of fluid flow past the radiation source. See, for example, any one of:
International Publication Number WO 2004/000735 [Traubenberg et al.];
International Publication Number WO 2008/055344 [Ma et al.];
International Publication Number WO 2008/019490 [Traubenberg et al.];
U.S. Pat. No. 7,408,174 [From et al.];
International Publication Number WO 10/069072 [Penhale et al.];
International Publication Number WO 10/102383 [Penhale et al.]; and
International Publication Number WO 11/014944 [Penhale et al.].
When these fluid treatment systems have been implemented there is an ongoing problem of build-up of fouling materials on the exterior surface of the radiation sources.
The prior art has focussed on this problem by allowing the fouling materials to build-up to a degree at which point the radiation source assemblies are removed for cleaning or an active cleaning system such as the one taught in the Maarschalkerweerd #2 Patents is used to remove the fouling materials by mechanical and/or chemical action.
While the cleaning system taught by the Maarschalkerweerd #2 Patents is a very significant advance in the art, there is room for improvement.
First, seal failure in the cleaning system taught by the Maarschalkerweerd #2 Patents can occur resulting in the loss of acidic cleaning fluid and a reduced capacity to remove the foulant as well as the introduction of the cleaning chemicals to the environment. Second, the cleaning system is relatively complex resulting in significant capital and operating costs associated with the equipment. Third, the mechanical cleaning equipment occupies space in the reactor which requires the UV lamps to have a minimum separation distance, which reduces the effectiveness of disinfection and lowers the efficiency of the ultraviolet radiation reactor. Fourth, the wiping action can cause scratches in the sleeves which may potentially promote fouling or lead to premature failure of the sleeve. Fifth, the moving parts required in the design may also lead to failure and maintenance requirements. Lastly, regardless of mechanical wiping, the sleeves ultimately must be removed for either cleaning and or replacement, which is time consuming and undesirable.
Therefore, a “passive cleaning” technique which provides continuous in situ cleaning without the use of mechanical devices and moving parts would be desirable.
U.S. Pat. No. 7,326,330 [Herrington et al. (Herrington)] teaches a passive cleaning technique wherein it is purported that biofilm formation and/or the deposition of fouling materials onto a quartz sleeve may be prevented by creating a locally low pH at the quartz sleeve. Apparently, this substantially increases the solubility of inorganic compounds (e.g., metal salts) which would otherwise precipitate onto the sleeve. The locally low pH is achieved by electrochemical means whereby a wire is wrapped about the quartz sleeve and connected to an electrical circuit such that the wire wrapped about the quartz sleeve becomes the anode. Inorganic compounds (e.g., metal salts) will precipitate at the cathode. The cathode may be de-scaled by cycling the polarity of the circuit.
However, the utility of the Herrington approach for prevention of ultraviolet radiation source assembly fouling is questionable. The locally low pH is believed to be created at the surface of the metal wire and not generally across the entirety of the quartz surface upon which fouling is occurring at the molecular level. In addition, the acidic species are subject to removal from the sleeve interface due to the strong convection environment in the reactor. Moreover, the Herrington approach produces scale on the cathode which requires cleaning—i.e., the build-up of fouling materials is simply transferred from one surface to another. Furthermore, the process requires the consumption of additional energy at great cost to achieve the passive cleaning process. Herrington suggests that diamonds may be used to improve electrical contact with the quartz surface—this is obviously an impractical and costly solution. It is also possible that the wrapping of a metal wire about a quartz sleeve may exacerbate fouling by trapping debris. Thus, it would be desirable have an approach that obviates the need of electrical contacts and the need for external energy supply by utilizing a quartz sleeve which possesses inherent strong surface acidity throughout the entirety of the surface thus obviating the need for an external means to generate acidity at the interfacial region.
U.S. Pat. No. 7,425,272 [Butters et al. (Butters)] teaches cleaning of ultraviolet radiation protective sleeves using an abrasive and optionally acidic slurry which passes through the reactor. It is taught that the abrasive material, in combination with locally high shear stress, physically removes the foulant from the protective sleeves. Optionally, the slurry may be made acidic by the mixing of an acid with the decontamination mixture thus enabling the release of the foulant by solubilizing the deposited metal and other oxide layers. In another embodiment, the abrasive material possesses photocatalytic properties, which promote oxidation reactions and is claimed to clean the UV sleeves. However, in each of these approaches, the abrasive material must be recovered from the decontaminated water, which requires material separation, material handling and the associated capital and operating costs. Most undesirable is the fact that the introduction of acid to the water will necessitate a downstream neutralization step or another means to recover the acid from the decontaminated water before discharge to the environment. In addition, since a large volumetric flow rate of water is processed in decontamination facilities, a large volumetric flow rate of strong acid would be required to achieve a sufficiently low pH to dissolve inorganic metal and other oxide layers.
Thus, despite the advances in the art, it would be highly advantageous to be able to configure the surface of the radiation source assembly (particularly the quartz sleeve or other protective surface for the ultraviolet radiation source) on which fouling materials build-up to obviate or mitigate the actual build-up of fouling materials. In other words, it would be desirable to have an approach that reduces the build-up of the fouling materials in the first instance. It would be further advantageous if the approach was relatively low cost and maintenance free for the user of the ultraviolet radiation fluid treatment system.